The invention relates to a process for producing the reversible or removable assembly of an electronic read and/or operating circuit with an optionally electrically conductive support. More specifically, the invention relates to a process for the assembly of an electronic read and/or operating circuit combined with a detection circuit, with an enclosure having predetermined physical characteristics, especially in respect of temperature.
Although more specifically described within the framework of infrared detectors, the process according to the invention would not have to be restricted to this single embodiment. Any other application of this process of course falls within the field of protection of this invention.
Infrared detectors conventionally function at low temperature, that is to say within a temperature range of between 50 and 130 kelvin (K). In this way, the detectors proper are combined with a cryostatic chamber (cryostat), the cold finger of which contains liquid nitrogen or liquid air, depending on their use temperature, or a cryogenerator device.
The detection device proper fundamentally consists of a first circuit, termed the detection circuit, comprising a specific number of photosites produced collectively by microelectronic techniques on a semiconductor material sensitive to infrared radiation. This electronic detection circuit is in permanent heat exchange with the cryostat, this exchange being effected via a cold finger.
The utilisation of photon radiation detected by this circuit takes place at the level of a read circuit which is associated with it, this read circuit also being in permanent heat exchange with the cryostat.
Traditionally, the connections between the detection circuit and the read and/or operating circuit are made either by connecting wires or by a collective solder using indium microspheres.
This latter technique, the preferred field of application of the invention, makes it possible to illuminate the detection circuits from their rear face, in fact avoiding the use of any bulky connections, which is not very practical in use.
The system comprising the detection circuit connected to the read and operating circuit is conventionally termed "detection block".
This detection block, in permanent heat exchange with the cold plane of the cryostat, is kept mechanically and thermally in contact with the latter via an interface generally consisting of an insulating support of the ceramic type, the bond between this support and the detection block being produced by means of a conductive adhesive bond, formed, for example, of epoxide resin containing metal fillers intended to ensure electrical conduction between the rear face of the detection block and more precisely of the read and operating circuit and the cryostat connections. These connections generally consist of tracks engraved or screen-printed on the cold finger. In addition, the ceramic support is itself fixed on the cold plane of the cryostat by means of an electrically insulating adhesive bond, which typically is made of silicone.
For example, in FIG. 1 a diagrammatic representation of such an embodiment, constituting the prior art, has been shown. The cold finger (1) of the cryostat has at its upper end a cold plane (2) intended to ensure the heat exchange between the cryostat proper and the detection block (3, 4), corresponding, respectively, to the read and operating circuit (3) and to the detection circuit (4). In a known manner, the detection circuit (4) is electrically and mechanically connected to the read and operating circuit (3) by means of indium microspheres (15). As can be seen on this FIG. 1, a connecting substrate (5), made of an insulating material, typically of ceramic or of alumina, on which a network of conductive tracks (16) have been engraved or screen-printed, has been interposed between the cold plane (2) and the detection block (3, 4). This connecting substrate (5) is generally fixed on the cold plane (2) of the cryostat by means of a join of electrically insulating adhesive (6). The electrical connection between the engraved or screen-printed tracks (16) on the connecting substrate (5) and tracks engraved on and/or at the periphery of the cold plane (2) is conventionally produced by means of conductive microwires (17).
In addition, the electrical inputs and outputs, in particular on the front face of the detection block, are connected to the conductive tracks of the connecting substrate by means of conductive microwires (7), most often made of gold, which are soldered after sticking the detection block onto the connecting substrate. In addition, an electrical link is produced between the rear face of the detection block, and more particularly of the read and operating circuit (3) which face is in particular metallised, for example with gold, and the connecting substrate (5), said electrical link being produced by means of an electrically conductive adhesive (8).
Finally, the reference numeral (9) shows a conductive track engraved or screen-printed on the cold finger of the cryostat (1) and ending at an external connection block (10).